Capacitive keyboards typically have many switch keys which may be pressed and released to respectively define active and inactive switch states. Each switch key has a capacitive element that defines a low capacitance when the key is inactive and a relatively higher capacitance when the key is pressed. The change in capacitance of a key therefore indicates the operational state of the key.
Capacitive keyboards are desirable because of their structural simplicity and their associated relatively low manufacturing cost. Also, capacitive keyboards have a potentially higher reliability and a longer life then keyboards with keys that physically make and break conductive connections.
The above-referenced parent patent application Ser. No. 318,483, filed Nov. 5, 1981, shows several embodiments of an improved capacitive keyboard and associated switch keys that have many desirable features. One such embodiment of a switch key utilizes a spring to define a capacitance which indicates the operational state of the key. In operation, when the key is at rest, the spring is fully extended to define a minimum capacitance with respect to an underlying dielectric sheet and stationary capacitor plate. When the key is pressed, the spring is compressed so that its coils spread out over the dielectric sheet and the underlying capacitor plate. The compressed coils of the spring are disposed adjacent to the underlying plate and therefore define an increased capacitance for as long as the key is pressed.
The spring for each switch key of the disclosed capacitive keyboard is connected to an underlying printed circuit board by inserting a downwardly extending end of the spring into a plated hole of the board and soldering the end of the spring in the hole. In manufacturing such a capacitive key, the spring must first be carefully positioned on the printed circuit board and rotated until its downwardly extending end slips into its associated solder hole. If the keyboard has many keys, it can take a substantial amount of time to align and solder all of the springs to the board. The alignment process therefore adds to the cost of manufacturing.
Moreover, if the spring is rotated slightly when its end is in the printed circuit board, the body of the spring will move out of alignment with respect to its underlying capacitor plate and will therefore have to be realigned prior to soldering. Such realignment further reduces manufacturing efficiency and increases manufacturing costs.
Accordingly, it is an object of the invention to provide a relatively simple, inexpensive and rapid means for conductively affixing capacitive springs to a printed circuit board of a capacitive keyboard.
Another object of the invention is to provide a printed circuit board of a capacitive keyboard with plated holes that are positioned adjacent to the outer edge of the base of a capacitive spring to pass molten solder to the spring and thereby conductively connect the spring to the circuit board.
A further object of the invention is to provide a manufacturing process whereby capacitive springs may be easily aligned and conductively affixed to a printed circuit board of a capactive keyboard.
Another object of the invention is to provide a capacitive switch with a capactive spring which is positioned in relation to an underlying capacitive plate to maximize the difference between a switch capacitance defined when the spring is compressed and a switch capacitance defined when the spring is released.